Shortstopping vinyl chloride polymerizations with vinyl pyridines



i ate'nted Nov. 4,

SHORTS' IO PPING yiNyL eHLdRiInairoLiz- MERIZATIONS WITH VINYL PYRIDINES Dexter C. Seymour, ,Wyckofi, N. 11., 'a's'si'gnor to United States Rubber Company, N ew' York, N. Y, a corporation of New Jersey No Drawing. Application idly 10, 1951, Serial No. 2363063 '10 Claims. (01. zen-52.8

1 This :invention'relates' to improvements in vinyl chloride :polymerizations.

The polymerization of liquefied vinyl chloride is generally carried out atwmildly elevated temperatures, about 40 C. to 60 C,, in an aqueous medium "under a :pressure "substantially equal to its-saturated vapor pressure, =i.e. about 4 to 9 atmosphe'res, in the presence of a polymerization catalyst; Pressures referred 'to herein :are absolute i'pressures. The polymerization is generally carried toia range'o'f about 60% to 95 conversion of mononierfltbipolymer. Percentages and :parts referred-whereinare 'by weight. The polymerizatlonr'as'is well known maybe an emulsion'polymeilzation :(see Mark etfal. U; S. Patent 2,068,424, and German Plastics Practice by DeB'ell, Goggin &-Gloor, Pub. by DeBelland Richardson, SpringfieldyMass 1 946, pages57-66) or av granular polymefization -(see Lightfoot U. S. Patent. 2,511,593, andGerman Plastics Practice, pages 66-73, and the article by Ruebensaal 'on Vinyl Resins in Chemical Engineering. for December 1950, vol. 57,,1pages'l02 to 105) After conversion of the desired amount of monomerto polymer, residual unreacted monomeric vinyl chloride is removed and the polyvinyl chloride collected by various means-such as -'by coagulation or spray drying in the lease of aqueous emulsion polymerization, or by filtration in the cas' of aqueous granular polymerization. The resulting polyvinyl chloride is usually washed 'with water and dried. If the polymerization goes beyond the desired conversion a polymer ha-vin'gpropertiesinferior to those desired in the f nal product may result, particularly as regardsheat"and'light'stability.- To avoid this; the batch is generally cooled after the desired conversion Undesi'rable post-polymerizationmay also take place in the blow-down tank or in the "stripper Where unreacted vinyl chloride monomer is removed. At the end of the poly ,merization; it may be necessary to store or hold the polymer batch for some time without cooling before removing unrea'cted vinyl chloride monomer. In this case the-polymerization may con'- tinue during storage and thusgiv'e; a productof too hlgh conversion-and of resultant undesirable properties; Also, when the unreacted vinyl chloride monomer removed from the aqueous medium theremay be some vinyl chloride monomen, adsorbed on the polyvinyl chloride particles in theaqueous' medium, which is not removed until'dr yin'g" of the polyvinyl chloride. Thi adsorbedvinyl'chloride monomer may polymerize on the polyvinyl chloride particles before it can be reme'ved-gadyersely affecting the properties of the fin'ally'recovered polyvinyl chloride; Itis thereforefd'e'sirableto"add a material which acts to ter minate or shortstop the vinyl chloride poly merization-reaction after the desiredtpartialconversion of "polymerizable monomer to polymer has taken place and to prevent "any further polymerization of the residual unreacted viny1 "chloride' monomer; V

I have found that vinyl pyridines'are efiective shortstopping agents for vinyl chloride polymerizations. V In ea ryin iout the present invention, metmyi pyridine is added to the polymerization reaction after partial conversion of polyinerizable-monomer'to polymer (usually after about to conversion) and thereafter the unreacted vinyl chloride polymer is removed from the aqueous medium, and the polyvinyl chloride recovered in the usual manner. Examples of vinyl pyridines that may "be used are position isomers 2-vinyl pyridine, *3'-'viny1 pyridine,- and 4-vinyl pyridine, and position isomers having alkyl substituents in the pyridine ring 2-methyl=5-vinyl pyridine, 5- ethyl 2 vinylpyridine, 2,43- dim'ethyl- 6 vinyl pyridine, and mixtures thereof. Very small amounts of -su'ch'vinyl pyridines may'sa-tisfactorily be used to shortstop the polymerizationreaction; the amount effective to shortstop the-polymerize tioii generally being less than2% based on the originalIvinyl'ehloiidemonomer used. For pi'actidal purposes; the amount of shortstopper may bebet'ween 0.05% and 1% by weight of the original vinyl -chloridemc'non'ier used.

The polymerization reaction is carried out in the presence of a conventional free radical type polymerizationinitiater, such as a peroxygen' or azo' catalyst. Examples of peroieygen catalysts areinorgahic peroxides; e'. 'g. hydrogen p''roiiide and ersalts, such as alkali persul rates, alkali erborate's; alkali perarbonates; and organic peroxides, 'e. g. diacetyl peroxide, dibenzoyl peroxide, aeetyl benzoyl peroxide; lauroyl peroxide, cumehe hydroperoi'ri'd'e, tertiary'butyl hydroperox ide. of am cataly'st's are alpha, alpha- W I H nitrile and pmethoxybenzen diaz'o t-hi -"Z-naphth-yIether. Catalytic amounts from" 0.05% to 2% based on the vinyl chloride monomer-maybe used.

Tests 'showingthe' effectiveness of the chem icals of -the preseht inventi'on as shortstoppin'g agents for vinyl chloridepolymerization were carried out according to the following proced= ure: Into a Ca ins pressure tube was weighed ,o'f catalyst (alpha,

, 0.5328 g. 16.00325 o -er alpha' azobisisobutyronitrile) and th tube was sealed to a vacuum line. After evacuation to 0.0001 mm., 20.00 cc. (19.94 g., 0.319 mole volume measured at 30 C.) of pure vinyl chloride was distilled in and the tube was sealed off and heated at 30 C. for 4.5 hours. At the end of this time the contents were frozen in liquid nitrogen, the tube was opened, sealed to the vacuum line and evacuated. The unreacted vinyl chloride was distilled into a buret and its volume at 30 C. noted. From this was calculated the percent conversion before adding shortstop. Meanwhile, the tube was removed from the vacuum line and to it was added one weight percent on the original vinyl chloride of the chemical under test as a shortstop. The tube was rescaled to the vacuum line, its unreacted vinyl chloride was replaced, the tube was sealed off under vacuum and heated again at 30 C. for 4.5 hours. After the second heating period the tube was frozen, opened and sealed to the line as before. A final measurementof the volume of unreacted vinyl chloride was made and the percent conversion after adding shortstop was calculated. The difference between thesetwo conversions was taken as a measure of the shortstopping power of the compound under investigation. A control run without shortstop was carried out as a means of comparison. Results of these tests are shown in the following table:

Percent Conversion Increase in Final 4.5 hrs.

Percent Conversion at 9 hrs.

Percent Conversion Chemical Added after at 4.5 hrs.

2Vin l ridine 20.6 y Dy 14.1

20. 6 None (control) 31. 7 6

of liquid vinyl chloride, 1.3 parts of. emulsifying and buffering agents, and 0.2 part of potassium persulfate catalyst. The reaction vessels were agitated ina constant temperature bath at 45 C. for about '7 hours, at which time analyses showed a conversion of monomer to polymer of approximately 60%. At this point 0.5 part of 2-vinyl pyridine was added to one of the reaction vessels andno chemical was added to the other vessel (control polymerization). The agitation of the vessels inthe 45 C. bath was continued for hours more. At the end of this time analysis showed no increase in the 60% conversion where the 2-vinyl pyridine had been added, and substantially 100% conversion in the case of the control where no shortstop had been added.

The above work shows, the effectiveness of the chemicals as shortstopping agents in the dimcultly shortstopped early stages of bulk or mass oil-phase vinyl chloride polymerization, and in emulsion polymerization. The chemicals of the present invention are also effective as shortstoppers for granular polymerizations which may use inorganic water-soluble catalysts or organic monomer-soluble catalysts. polymerizations which use a monomer soluble catalyst are generally considered to be mass polymerizations of the individual liquid monomer globules. In aqueous emulsion and granular polymerizations, the'polymerization reaction is generally stopped at 60% to 95% conversion of monomer to polymer. In bulk polymerizations, the

In fact, granular v 4 polymerization reaction is generally stopped at lower conversions, e. g., around 40%. With the shortstopping agents of the present invention, the polymerization reaction may be stopped at any desired conversion.

In emulsion polymerizations, it is a simple matter to withdraw a sample from the reaction chamber from time to time and to analyze it for total solids in order to determine the percent conversion. On the other hand, it is almost impossible to follow the conversion in a granular polymerization by sampling, because the polymer formed separates so rapidly that a representative sample cannot be obtained. Thus other methods of determining the amount of conversion, and thereby the point at which the reaction should be stopped, must be used in following polyvinyl chloride granular polymerizations. For example, the heat evolved in the reaction mixture can be measured and be directly correlated with the extent of conversion via the known heat of reaction. Also, experience has shown that polyvinyl chloride of good physical characteristics may be obtained by stopping the reaction at the pressure drop which is at the point where the separate phase of liquid vinyl chloride monomers disappears (see German Plastics Practice, pages 61 and '77) In systems where the temperature in the reactor is automatically maintained by regulation of the jacket temperature, the pressure drop will beevidenced by a sudden pressure fall. In systems where the pressure in the reactor is automatically main-,

tained by regulation of the jacket temperature, the pressure drop will be evidenced by a rapid rise in jacket water temperature, whereupon the system is thrown out of automatic control and.

cooling water is introduced into the jacket resulting in the usual fall of pressure in the reactor.

Such methods other than sample analyses of de termining when to shortstop the reaction at the desired conversion may be used in emulsion polymerization as well as in granular polymerization. The evolution of heat or the viscosity characteristics may be followed in mass polymerization to determine the point at whichthe shortstopping.

agent should be added.

The following illustrates the. use of the short-.- stoppers of the present invention in batch aqueous; vinyl chloride polymerizations. A typical emulsion polymerization recipe which uses a water soluble catalyst parts of liquefied vinyl chlo.

ride, 200 parts of water, 0.2 part of potassium persulfate and 1.5 parts of surface-active emulsifying agent), or a typical granular polymerization recipe using awater-soluble catalystv (100 parts of liquefied vinyl chloride, 300 parts of Water, 0.3 1

part of potassium persulfate, and a small amount of buffering and wetting agents), or a typical granular polymerization recipe using a monomersoluble catalyst (100 parts of liquefied vinyl chloride, 300 parts of water, 0.5 part of lauroyl peroxide and a small amount of suspending agent). is agitated in a closed jacketed reaction vessel. The

batch is initially heated to the desired reaction 0.05 to 1 part of Z-Vinylpyridine, 3-vinyl pyridine;

l-vinyl pyridine, 2-methyl-5-vinyl pyridine, 5- ethyl z-vinyl pyridine, or 2,4-dimethyl 6-vinyl pyridine per 100 parts of original vinyl chloride used is added so that undesirable further polymerization is prevented. Alternatively, the shortstopping agent may be added at any desired conversion at the discretion of the operator. When the desired conversion has been reached and the shortstop added, the batch may be transferred to the blow down or storage tank, held there any desired length of time, and then transferred to the stripper when desired for removal of residual unreacted vinyl chloride monomer. Finishing operations after residual monomer removal are conventional as described in the literature references referred to above. The shortstopping agents of the present invention give a greater uniformity of .polymer properties, and also result in polymers having enhanced heat and light stability.

The shortstopp'ers of the present invention are applicable to shortstopping of modified vinyl chloride polymerswhich are made by copolymerizing a major proportion, generally over 80% of vinyl chloride and up to 20% of other monoolefinic material which is copolymerizable with vinyl chloride, such as a vinyl alkanoate, e. g. vinyl acetate, or vinylidene chloride, or an alkyl acrylate, e. g. methyl methacrylate, or an alkyl maleate, e. g. dimethyl maleate, diethyl maleate, isobutyl maleate, and mixtures thereof. Such polymerizations are similar to the homopolymerization of polyvinyl chloride but with a somewhat broader range of reaction temperatures from 25 C. to 100 0., depending on the particular vinyl chloride copolymer being made (see "German Plastics Practice, pages 76-78). The same amount of shortstopping agent based on the amount of vinyl chloride employed may be added after partial conversion, generally at about 60% to 95% conversion of polymerizable monomeric material to polymeric material.

In view of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection afforded the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of a vinyl pyridine in which any substituents are alkyl ring substituents to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

2. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by Weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of vinyl pyridine selected from the group consisting of 2- vinyl pyridine, 3-vinyl pyridine, l--vinyl pyridine, 2-methyl-5-vinyl pyridine, 5-ethyl-2-vinyl pyridine, and ZA-dimethyl-G-vinyl pyridine to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

3. In the process of preparing a vinyl chloride polymer by the polymerization for material of the group consisting of vinyl :chloride 'and mixturesioi' vinyl chloride with up to 20% by weight of the vinyl chlorideyof other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of 2-vinyl pyridine to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material. 7

4. In the process of preparing polyvinylchloride by the polymerization of vinyl chloride ii-i "anaqueous medium, the step comprising adding- 0.05% to 1% of a vinyl pyridine in which a'n'y substituents are alkyl ring substituents-based on the weight of the monomeric vinyl chloride being used to the reaction mixture during :po11ymer1za' tion to stop the same after about 60%-to conversion of vinyl chloride monomer to polyvinylchloride.

5. The method of preparing a vinyl chloride polymer which comprises subjecting material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material Which is copolymerizable with vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a polymerization catalyst, and after about 60% to 95% conversion of polymerizable monomeric material to polymeric material adding to the polymerization reaction 0.05% to 1 based on the weight of the original monomeric vinyl chloride used of a vinyl pyridine in which any substituents are alkyl rin substituents to stop polymerization of unreacted polymerizable monomeric material, and thereafter removing unreacted polymerizable monomeric material from the aqueous medium.

6. The method of preparing a vinyl chloride polymer which comprises subjecting material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by Weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a polymerization catalyst, and after about 60% to 95% conversion of polymerizable monomeric material to polymeric material adding to the polymerization reaction 0.05% to 1% based on the weight of the original monomeric vinyl chloride used of vinyl pyridine selected fromthe group consisting of 2-viny1 pyridine, 3-vinyl pyridine, 4-vinyl pyridine, 2-methyl-5- vinyl pyridine, 5-ethyl-2-vinyl pyridine, and 2,4- dimethyl-G-vinyl pyridine to stop polymerization of unreacted polymerizable monomeric material, and thereafter removing unreacted polymerizable monomeric material from the aqueous medium.

'7. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a peroxygen catalyst, and after partial conversion of vinyl chloride monomer to polyvinyl chloride adding to the polymerization reaction a small amount of a vinyl pyridine in which any substituents are alkyl ring substituents to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

8. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in an aqueous medium at a temperature between 40 C. and 60 C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of a vinyl pyridine in which any substituents are alkyl ring substituents to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

9. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in an aqueous medium at a temperature between 40 C. and 60 C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of vinyl pyridine selected from the group consisting of 2-vinyl pyridine, 3-vinyl pyridine, 4-vinyl pyridine, 2-methyl-5-vinyl pyridine, 5-ethyl-2-vinyl pyridine, and 2,4-dimethyl-6-vinyl pyridine t6 stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

10. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in an aqueous medium at a temperature between C. and C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of 2- vinyl pyridine to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

DEXTER C. SEYMOUR.

No references cited. 

1. IN THE PROCESS OF PREPARING A VINYL CHLORIDE POLYMER BY THE POLYMERIZATION OF MATERIAL OF THE GROUP CONSISTING OF VINYL CHLORIDE AND MIXTURES OF VINYL CHLORIDE WITH UP TO 20% BY WEIGHT OF THE VINYL CHLORIDE OF OTHER MONOOLEFINIC MATERIAL WHICH IS COPOLYMERIZABLE WITH VINYL CHLORIDE, THE STEP COMPRISING ADDING A SMALL AMOUNT OF A VINYL PYRIDINE IN WHICH ANY SUBSTITUENTS ARE ALKYL RING SUBSTITUENTS TO THE REACTION MIXTURE DURING POLYMERIZATION TO STOP THE SAME AFTER PARTIAL CONVERSION OF POLYMERIZABLE MONOMERIC MATERIAL TO POLYMERIC MATERIAL. 